1. Field of the Invention
The present invention relates to an image forming apparatus operable in a plurality of color modes.
2. Description of the Related Art
Hitherto, in an electrophotographic image forming apparatus, there has been demanded reduction in a first print out time from instruction of printing to output thereof, and in a first copy time from depression of a copy key to copy output. Further, as one method of the time reduction, there has been widely known a technology of performing an image formation preparing operation before the instruction of the printing or copying (image forming instruction) is input.
In U.S. Pat. No. 5,107,279, there is proposed a configuration in which, when an operation from which a start of image formation is predicted, such as an operation of an operating portion of the image forming apparatus and placement of an original on an original reading device, is detected, a motor for a rotary polygon mirror is started to be rotated prior to the image forming instruction. In general, a period of time from the start of the rotation of the motor for the rotary polygon mirror to stabilization of a rotation speed thereof is longer than that of a drive motor for an image bearing member or other motors required for the image formation. In view of the above, the motor for the rotary polygon mirror is started to be rotated prior to the image forming instruction, thereby being capable of reducing the period of time from the image forming instruction to the start of the image formation. With this, the image formation can be started in a shorter period of time after the image forming instruction without causing a user to wait for a long period of time from the start of the rotation of the motor for the rotary polygon mirror to the stabilization of the rotation speed thereof.
In recent years, the image forming apparatus has been operable in a monochrome mode for forming a monochrome image, and in a full-color mode for forming a full-color image.
However, in the related art, irrespective of a set color mode (monochrome mode or full-color mode), the same image formation preparing operation has been performed. Therefore, the conventional image forming apparatus may become disadvantageous from the viewpoint of the reduction in the first print out time and power saving.